The present invention relates to methods of treating adult onset diabetes by administering to a patient in need thereof an effective amount of a lectin capable of inducing a decline in food intake and inducing hypoglycemia. The present invention also relates to methods of inducing weight loss by administering an effective amount of a lectin capable of inducing a decline in food intake and repeating the administering step to maintain the decline in food intake. In particular, the present invention relates to the methods of treating adult-onset diabetes and inducing weight loss with the mixture of lectins known as pokeweed mitogen and the bitter pear melon lectin.
Adult-onset Type II diabetes mellitus is a major health problem in this country. Because it is exacerbated by obesity, treatment of this disease is often two-pronged, using drugs to maintain normal blood glucose concentrations and diet therapy to promote weight loss. However, current hypoglycemia drugs are not always effective, and adherence to diet therapy is generally poor.
Lectins are a general class of proteins that bind to carbohydrates. The binding of these lectins to carbohydrates that are part of cell membrane receptors can result in cell activation. This is particularly well characterized with cells of the immune system. Lectins are widely used to stimulate immune function in in vitro studies.
The crude extract of the lectins from the pokeweed plant, Phytolacca americana is referred to as pokeweed mitogen. Pokeweed mitogen is a mixture of five lectins, which are designated as Pa-1 to Pa-S. These range in size from 19 to 30 kD, and contain approximately 3 percent carbohydrate. The ligand for all the pokeweed lectins is N-acetyl glucosamine. Despite binding to the same ligands, there is a disparity between the bioactivity of the five pokeweed mitogen lectins. Only Pa-1 is a polymer, and only Pa-1 stimulates B cells. Further, Pa-2 to Pa-5, all of which stimulate T cells, do so with widely differing potency.
Effects attributed to pokeweed mitogen include stimulation of the immune system, with the appearance of plasma cells in the peripheral circulation, the release of interferon-y and tryptophan metabolites, and transient splenomegaly secondary to blood engorgement. Zazula et al., P.S.E.B.M., 133, 1088-92 (1970), disclosed that the intravenous injection of pokeweed mitogen to mice produced a marked increase in the weight of the spleen, with an increase in the number of nucleated cells, lymphoblasts, and mitotic figures. A marked increase in the total number of plasma cells was also produced, but these cells did not appear in the peripheral blood, and the effect of pokeweed mitogen was limited to a transient leukopenia. One to three days after the administration of pokeweed mitogen at a level of 175 mg/kg, all mice lost an average of 1.5 g of body weight, but by day five showed a net weight gain. Weight loss following pokeweed mitogen infusion is not consistently reported in the literature.
Wheat germ agglutinin is a lectin that shares structural and binding properties with pokeweed mitogen lectins. Mice given wheat germ agglutinin developed a non-significant hypoglycemia and a decline in food intake, but no weight loss. Like Pa-2 to Pa-5, wheat germ agglutinin stimulates T cells.
There exists a need for a pharmaceutical composition for the treatment of diabetes mellitus that produces both a lowered circulating glucose level and an anorexic state that results in the loss of body weight.